1. Field of the Invention
The present invention relates to a weathering test apparatus for conducting weathering tests and light-fastness tests and, in particular, to an apparatus using an air-cooled metal halide lamp as a radiant energy source for the weathering tests.
2. Description of the Related Art
As to the kinds of radiant energy sources of a weathering test apparatus that tests the weatherability and the color fastness of materials, common ISO/JIS standards describe an enclosed carbon arc lamp, a sunshine carbon arc lamp, and a xenon arc lamp. In the weathering test and the light-fastness test, the correlation between the outdoor or indoor exposure test and the accelerated test with an apparatus is important to determine the life and durability of materials and products.
Thereupon, each radiant energy source spectrum simulates the sunlight spectrum by means of a combination of various kinds of glass filters. For example, the radiation at wavelengths less than 275 NM is cut off in the case of an exterior materials test, and the radiation at wavelengths less than 295 NM is cut off in the case of an interior materials test.
However, as the weatherability and the light-fastness of materials and products have been improved in recent years, a longer period of time is required to obtain a test result. And thus, it is necessary to provide a more accelerated weathering test apparatus.
Therefore, interest in a weathering test apparatus that a metal halide lamp as the radiant energy source is increasing. This is because the metal halide lamp produces radiation energy that is approximately 30 or more times stronger from 300 NM to 400 NM than that of the above described enclosed carbon arc lamp, sunshine carbon arc lamp, and xenon arc lamp.
The weathering test apparatus with the metal halide lamp is primarily used for a screening test. The metal halide lamp may include an air-cooled type and a water-cooled type. And the kind of lamp housing for the lamp can be an air-cooled type and a water-cooled type. Further, a metal halide lamp whose rating is 2 kW, 4 kW, 6 kW is generally used. The metal halide lamp is a long-arc straight-tube style air-cooled type, and the associated tube is small. The lamp is used in a horizontal position. Also, the lamp housing that cools the lamp with water has a double-tube structure and includes an inner optical filter and an outer optical filter, which arrange a spectral distribution of the radiant energy source. The above-mentioned general weathering test apparatus with the metal halide lamp is a combination of the air-cooled lamp and the water-cooled lamp housing.
Japanese Patent No. 2,942,444 describes two types of weathering test apparatuses using the above-mentioned long-arc type air-cooled metal halide lamp and the above-mentioned water-cooled lamp housing. The first type of weathering test apparatus, wherein the lamp is horizontally positioned in an upper portion of a test chamber and a specimen stage is horizontally fixed on a lower portion of the test chamber. The second type of weathering test apparatus, wherein the lamp is horizontally located in approximately the center of the test chamber and a horizontal specimen rack rotates about the lamp.
The prior art apparatus, however, does not include a weathering test apparatus that uses a vertically disposed long-arc type metal halide lamp. It is difficult to use the conventional long-arc type metal halide lamp in a vertical orientation, because halide metals in the lamp accumulate in a lower portion of the lamp, and thus the spatial distribution curve of luminous intensity becomes uneven.
Some short-arc and low wattage type metal halide lamps are used in a vertical orientation. The maximum radiation length of the short-arc type is 3 cm. However, the short-arc type is for illumination and point-source light. Therefore, the radiant energy of the visible radiation part is too strong for an effective weathering test. Also, it is necessary to put specimens on the small spherical spatial distribution curve of luminous intensity, but practically speaking, this is rather difficult. In particular, it is difficult to use the conventional short-arc type vertical metal halide lamp by extension of the radiation length for weathering tests, because the lamp cannot be properly cooled. A radiation tube of the lamp is disposed inside an outer tube of the lamp, and heating. Therefore, halide metals in the lamp tend to gather in a lower portion of the lamp and a spatial distribution curve of luminous intensity becomes uneven.
Also, in the case of weathering tests, the spectral energy distribution of the radiant energy source must simulate the spectral distribution of sunlight. And so, glass filters are always needed to arrange the spectral distribution. The lamp housing, which is not only a water-cooled type but also an air-cooled type, is necessarily a double-tube structure comprising the inner optical filter and the outer optical filter. In the case of the water-cooled type, the filters provide a flow of cooling water and a specified spectral energy distribution. In the case of the air-cooled type, the filters provide a flow of cooling air and a specified spectral energy distribution.
The above-mentioned water-cooled lamp housing is a more complex structure than the air-cooled type, but nevertheless has a high cooling efficiency.
However, when the long-arc type air-cooled vertical metal halide lamp whose rating 2 kW or 3 kW is lighted in the above double-tube structure type lamp housing, the life of the lamp is very short.
As a result, we analyzed the lamp having a short life, and found that the molybdenum thin film in a lower seal portion of the lamp, which acts as the electric conductor between the electrodes and a lead wire, is damaged or the lower electrode of the lamp changes to an abnormal color, i.e. the lower electrode becomes blackened, and some parts of tube are damaged. As mentioned above, the abnormally discolored portion was concentrated on the lower part of the lamp.
Applicant measured the temperature at three locations of the lamp housing, i.e. an air entrance, an upper seal portion of the lamp, and a lower seal portion of the lamp. And, as a result of several measurements, it was discovered that the temperature difference between the upper seal portion of the lamp and the lower seal portion of the lamp exceeded 100xc2x0 C. The reason for the temperature difference is that the temperature of warmed air in the upper seal portion of the lamp increases due to the heat of a radiation part while warm air passes through the radiation part and reaches the lower seal portion of the lamp.
Then, Applicant tried to increase the cooling air volume from a blower. As a result, the temperature of the upper seal portion of the lamp and the temperature of the lower seal portion of the lamp were reduced. However, it is impossible to solve the problem of the temperature difference between the upper seal portion of the lamp and the lower seal portion of the lamp by increasing the cooling air volume. The temperature difference creates an abnormal convection in the tube. The abnormal convection causes an abnormal temperature distribution in the radiation part and an adhesion of the enclosed halide metals to the lower electrode. The abnormal temperature distribution in the radiation part causes an abnormal spatial distribution curve of luminous intensity, in other words, abnormal lighting. The abnormal lighting results in incorrect test results. Accordingly, the test accuracy of the device is reduced.
It is an object of the present invention to provide a weathering test apparatus which comprises a long-arc type air cooled vertical metal halide lamp and a lamp housing for the lamp and a vertical specimen rack which rotates about the lamp, which is centrally located in the housing.
To this end, Applicant has developed a new weathering test apparatus having a long-arc type air-cooled metal halide lamp in which halide metals and mercury and a rare gas are infused. The lamp comprises a supporting member having at least one hollow protrusion positioned at the upper half to upper two thirds of the radiation length of a radiation tube wall. The radiation length of the lamp is 5 cm to 15 cm. The lamp lights in a vertical orientation.
Also, an inner ring of a lower metal fitting is mounted to the lamp housing.
A cooling device is positioned in the inner ring of the lower metal fitting. The cooling device is capable of adjusting the volume of air from an air supply device, located outside of the test chamber, and cooling the lower seal portion of the lamp by blowing cooling air. The inner ring of the lower metal fitting is located between an inner optical filter and the lower seal portion of the lamp. The cooling device is positioned such that cooling air impinges on the center of the lower seal portion of the lamp. By the present invention, the cooling device decreases the temperature difference between the upper seal portion of the lamp and the lower seal portion of the lamp.
If the cooling device is positioned at an upper part of the lower seal portion of the lamp, it is possible to influence the temperature distribution in the radiation part of the lamp, and to cause an unstable radiation energy distribution. Also, in the case where the cooling device is positioned at the lower part of the lower seal portion of the lamp, the cooling device is only able to cool the bottom of the lower metal fitting. However, when the cooling device is positioned at the lower part of the lower seal portion of the lamp, the cooling device is not able to decrease the temperature difference between the lower seal portion of the lamp and the upper seal portion of the lamp.
The air volume of the blower can be selectively adjusted in order to send cooling air into the space between the lamp and the inner optical filter. Also, the air volume of the air supply device mounted outside the test chamber can be selectively adjusted to send cooling air to the cooling device.
In the case of the air-cooled type lamp housing, the lamp is cooled by open-air, the changing of the open-air temperature, and the air volume to influence the cooling capability. Therefore, an air volume adjustment device is added to selectively adjust the air volume in order to maintain the proper temperature of the upper seal portion of the lamp and the proper temperature of the lower seal portion of the lamp. Further, in the case of the air-cooled type lamp housing, dust that is suspended in air will be inhaled by the cooling device, and thus, the dust soils the lamp and the filters. Therefore, it is necessary to attach an air filter on the blower and the air supply device.